THE EFFECTIVENESS OF REBURNING USING RICE HUSK AS SECONDARY FUEL FOR NO_X REDUCTION IN A FURNACE

ABSTRACT

The aim of the present work was to evaluate the effectiveness of the reburning process using biomass (rice husk) as reburn fuel in a large-scale laboratory furnace. For comparison purposes, tests were also conducted using natural gas and ethylene as reburn fuels. The paper reports new data for flue-gas emissions for a wide range of experimental conditions which quantify the effects of the reburn fuel fraction (energy basis), residence time in the reburning zone, and initial NO _x concentration for the three secondary fuels on NO _x reduction from the present combustor. The results show that at reburn zone residence times of about 0.7 s the reburning performance of the rice husk (1) is comparable to that of the natural gas reburning at high reburn fuel fractions, with almost 60% NO _x reduction achievable at reburn fuel fractions of 25 and 30%, and (2) approaches those of the natural gas and ethylene at high initial NO _x concentrations, with nearly 60% NO _x reduction attainable at initial NO _x concentrations between around 500 and 970 ppm. The results also reveal that there is a correlation between the extent of NO _x reduction and particle burnout: the higher the reduction, the lower the burnout. However, the present results combined with previous data from the same furnace using coal as reburn fuel suggest that the use of rice husk as reburn fuel in full-scale equipment would have a lower impact in the carbon burnout as compared with coal.

Keywords:

• NO _x emissions
• reburning
• rice husk
• natural gas
• ethylene

Acknowledgments

This work was developed within the framework of project number POCTI/EME/37529/2001, which is financially supported by Fundação para a Ciência e a Tecnologia under the programme Programa Operacional “Ciência, Tecnologia, Inovação” (POCTI) (59% of the funds from Fundo Europeu de Desenvolvimento Regional (FEDER) and 41% from Orçamento de Estado (OE)). The authors also thank technician Manuel Pratas who was very generous with his valuable assistance during all the stages of the work presented herein.